Field of the Disclosure
The present disclosure relates to ophthalmic surgery, and more specifically, to mechanical support of an indirect contact lens by a surgical microscope during vitreoretinal surgery.
Description of the Related Art
In ophthalmology, eye surgery, or ophthalmic surgery, is performed on the eye and accessory visual structures. More specifically, vitreoretinal surgery encompasses various delicate procedures involving internal portions of the eye, such as the vitreous humor and the retina. Different vitreoretinal surgical procedures are used, sometimes with lasers, to improve visual sensory performance in the treatment of many eye diseases, including epimacular membranes, diabetic retinopathy, vitreous hemorrhage, macular hole, detached retina, and complications of cataract surgery, among others.
During vitreoretinal surgery, an ophthalmologist typically uses a surgical microscope to view the fundus through the cornea, while surgical instruments that penetrate the sclera may be introduced to perform any of a variety of different procedures. The surgical microscope provides imaging and optionally illumination of the fundus during vitreoretinal surgery. The patient typically lies supine under the surgical microscope during vitreoretinal surgery and a speculum is used to keep the eye exposed. Depending on a type of optical system used, the ophthalmologist has a given field of view of the fundus, which may vary from a narrow field of view to a wide field of view that can extend to peripheral regions of the fundus. For many types of vitreoretinal surgery using the surgical microscope, the surgeon may desire to have a very wide field of view of the fundus that extends beyond the equator and even out to the ora serrata. The optical system to provide the view of the fundus to the surgeon during vitreoretinal surgery may include a special ocular lens, of which three types are typically used: a direct (plano, flat, or magnifying) contact lens, an indirect non-contact lens, or an indirect contact lens.
A contact lens is in physical contact with the cornea and therefore has a concave surface to match the convex surface of the cornea. Typically a small amount of refractive index-matching gel or fluid resides between the cornea and the contact lens to prevent unwanted extraneous interfacial reflections and to protect the cornea from dehydration.
A non-contact lens does not touch the eye and is spaced a certain working distance away from the eye.
A direct lens creates a non-inverted virtual image of the fundus behind the eye lens and generally in front of the fundus. The surgeon uses the surgical microscope to focus directly on this non-inverted virtual image, which is also referred to as an intermediate image plane or a focus plane. The direct lens enables the surgeon to directly view the fundus.
An indirect lens creates an inverted real image in the intermediate image plane in front of the eye lens (between the eye lens and the surgical microscope) and the surgeon uses the surgical microscope to focus on this intermediate image plane. The indirect lens enables the surgeon to indirectly view the fundus via the intermediate image plane. Since the indirect lens image is inverted to the viewer looking through the surgical microscope, typically an inverter lens is added to the surgical microscope to re-invert the fundus image to match the physical orientation of the eye during vitreoretinal surgery.
A direct contact lens can be placed onto the eye and is generally thin enough axially to normally remain in place on the cornea during vitreoretinal surgery. In certain optical systems, direct contact lenses have self-stabilizing features on the lens, such as base extensions that assist in keeping the direct contact lens from moving during surgery. However, a direct contact lens may not provide a very wide field of view into the fundus and of the retina and the field of view may be limited to about 30 degrees.
An indirect non-contact lens is not in contact with the eye and may be fixed to the surgical microscope. Therefore, the indirect non-contact lens may avoid issues of positional instability and additional resources involved (such as having a skilled surgical assistant to hold or reposition the lens) during vitreoretinal surgery. At least for these reasons, the indirect non-contact lens may be the ophthalmic surgical lens often chosen by many ophthalmologists. However, an indirect non-contact lens may be limited in the field of view of the fundus provided to the surgeon during vitreoretinal surgery. For example, the field of view using an indirect non-contact lens may be limited to less than about 140 degrees (full angle) and may be about 10 degrees less than wide angle contact lenses.
In order to see beyond the region of fundus viewable at one time with the indirect non-contact lenses, the surgeon may employ various techniques during vitreoretinal surgery. For example, the surgeon may indent a peripheral region of sclera to push the fundus in the affected region into the field of view. The surgeon may rotate the eye off the optical axis to direct the field of view onto the desired peripheral region. In some instances, a combination of techniques is used. Frequently rotating the eye or depressing the sclera to view peripheral regions of the fundus are extraneous operations during vitreoretinal surgery that are performed for the purpose of obtaining a sufficient view and do not contribute to the primary treatment purpose of the surgery. Such extraneous operations may result in additional trauma for the patient, increased time of surgery, and increased likelihood of surgical complications and may be undesirable for at least these reasons.
An indirect contact lens may provide a much greater field of view of the fundus than other types of ophthalmic surgical lenses. Indirect contact lenses may provide a field of view up to about 170 degrees (full angle), essentially out to the very edge of the retina at the ora serrata in a single image. However, indirect contact lenses, which rest on the cornea during vitreoretinal surgery, are generally top-heavy due to their optical construction and typically move in angular and positional orientation after initial placement on the eye. Indirect contact lenses may also be relatively sensitive to small movements by the patient during surgery, which is undesirable. Therefore, the surgeon oftentimes engages the help of an assistant, either to continually hold the indirect contact lens in place or to frequently reposition the indirect contact lens many times during the course of vitreoretinal surgery. Despite the large field of view afforded, the lack of positional stability and the additional involvement of a skilled surgical assistant to position the lens may be undesirable. At least for these reasons, the free-standing indirect contact lens may be an unpopular choice among vitreoretinal surgeons.